The present invention relates generally to a semiconductor device, and more particularly to a device that protects an internal circuit of a semiconductor device from damage resulting from electrostatic discharge (ESD).
Generally, an electrostatic discharge phenomenon is sorted according to the cause of the electrostatic generation. In other words, they are sorted as a human body model (HBM) where static electricity is generated by means of a human body, a machine model (MM) where static electricity is generated by means of contact with some sort of measuring equipment, and a charge device model (CDM) where static electricity accumulated in an element makes external contact to instantly generate static electricity.
Such static electricity flows intensively through any weak portions of a semiconductor device to melt junction or contact parts of an internal element or a gate oxide film, etc. causing failure of a semiconductor device. In particular, as manufacturing techniques for semiconductor devices develops, a thickness of a gate insulating film of a transistor that constitutes an input/output buffer has become thinner so that a voltage capable of destroying a gate insulating film is lowered.
Therefore, studies are being performed to lower an operating voltage of a device in order to protect a semiconductor device from electrostatic discharge.
FIG. 1 is one example of a device to protect a semiconductor device from electrostatic discharge according to the prior art. An example of an operation of electrostatic discharge, static electricity inputted through an input/output terminal 15 is discharged and transferred to a power voltage line VCC through a transfer means 11 configured of diodes. The static electricity that is transferred to the power voltage line VCC is detected by a detection means 12 configured of a resistance element R1 and a capacitor C1 coupled in series between the power voltage line VCC and a ground voltage line VSS. The detected voltage is amplified by a driving means 13 to operate a discharge means 14. Therefore, the power voltage line VCC and the ground voltage line VSS are intercoupled so that the static electricity input to the power voltage line VCC is discharged to the ground voltage line VSS.
The protection device of FIG. 1 as described above detects a voltage drop in the detection means 12 corresponding to an alternating current in the early stage of electrostatic generation to drive the discharge means 14 in order to increase an operation speed of the electrostatic discharge protection device of the semiconductor device. However, since the voltage drop detected by the detection means 12 is limited to a rising interval of the static electricity, it is difficult to detect the voltage drop from other intervals of electrostatic generation, e.g., a peak interval or a falling interval of the static electricity that may result in internal circuit 16 being damaged.
Devices have been disclosed to protect a semiconductor device from electrostatic discharge utilizing a detection means including a resistor and diode to account for such problems as mentioned above. However, the detection means detect a voltage drop when the operating voltage of the diode is applied, but an operation when the electrostatic current becomes smaller than the operating voltage of the diode is not sufficient to prevent damage to an internal circuit.